1. Field
This disclosure relates generally to semiconductor devices, and more specifically, to Gallium Nitride (GaN) metal insulator semiconductor heterostructure field effect transistors (MISHFETs) and metal oxide semiconductor heterostructure field effect transistors (MOSHFETs).
2. Related Art
As electric power systems in cars, appliances, and other commercial and industrial applications demand higher and higher efficiency, this increases the demand for highly efficient DC to AC power inverters and DC to DC boost converters. Such inverters and boost converters require high efficiency transistors. Gallium nitride (GaN) transistors have started to emerge as the technology of choice for highly efficient transistors with low on-resistance and extremely high breakdown voltage. Transistors derived from AlGaN/GaN heterostructures enjoy high breakdown and low on-resistance because GaN has inherently high breakdown field strength and AlGaN/GaN heterojunctions have very high electron sheet density. The high breakdown field strength and high electron sheet density arise from the wide 3.4 eV bandgap of GaN. This bandgap is much wider than competing semiconductor technologies such as Si with a 1 eV bandgap and GaAs with a 1.6 eV bandgap.
Power devices generally require that the ratio to the on-current to off-current have a value of 107 or greater since at very high voltages, even a small amount of drain leakage current at a high standby voltage—for example 500-1000 V or even higher—consumes a large amount of power. As a result, the efficiency then suffers. In a field effect transistor, gate leakage can dominate drain leakage; negative gate current predominately manifests itself at the drain contact.